1. The Field of the Invention
The present invention relates to tunable vertical cavity surface emitting lasers. More particularly, embodiments of the present invention are concerned with methods for producing a tunable vertical cavity surface emitting laser that uses an electrostrictive polymer having a holographic optical element with a narrow filter function.
2. Background and Related Art
Vertical cavity surface emitting lasers (VCSELs) are an example of semiconductor lasers that are used in optical fiber systems. VCSELs have several advantages over other types of semiconductor lasers. VCSELs can be manufactured in large quantities due to their relatively small size and can often be tested on a single wafer. VCSELs typically have low threshold currents and can be modulated at high speeds. VCSELs also couple well with optical fibers.
VCSELs typically emit wavelengths on the order of 0.85 microns. VCSELs that operate at single wavelengths or at longer wavelengths on the order of 1.3 to 1.55 microns, which are more useful in optical communications systems, are very difficult to manufacture or fabricate. The difficulty in fabricating VCSELs that generate light in a single mode and/or at longer wavelengths is often related, for example, to the atomic lattice structure of the materials, the quality of the active region or gain medium, the reflectivity of the mirror systems, and the material composition.
Another problem with VCSELs is related to their tunability. Tunable semiconductor lasers are very useful, especially in wavelength-division multiplexing (WDM) systems. When fixed wavelength lasers are used in WDM systems, it is necessary to have a separate VCSEL for each wavelength. For example, a 100 channel WDM system requires 100 different VCSELs. This leads to a number of different problems from maintaining an adequate inventory for spare parts to producing and testing VCSELs of varying wavelengths. A tunable laser can alleviate many of these expensive issues.
In general, tunable lasers often suffer from needing a long gain cavity in order to generate sufficient gain. From a tuning perspective, the long cavity is extraneous and complicates the tuning functionality because the modes of the gain cavity, for example, must be kept in a fixed relationship with respect to the tuning element. Thus, many tunable lasers require a phase adjust section. VCSELs have the desired short cavities, but the gain for single mode VCSELs is insufficient to allow generation of optical power in the multi-milliwatt range. Increasing the diameter of the VCSEL aperture to increase power also results in multi mode emission.